Do you always need a root canal before you have a tooth crown?

No.

If the nerve is good and it's not compromised when filling the tooth then you can get just a crown. I have one.

If the nerve gets compromised, then you need both a root canal and a crown.

Fillings can sometimes be done through the crown.

I hate when the crown has to be removed because of decay on the edge of the bottom portion if the crown.

If there is no sign of infection at the tip of the root and you are having no symptoms of infection then no, a root canal is not necessary before a crown. Often a crown is placed on a tooth that has a large filling to make it more stable. That being said, sometimes after a crown has been placed, the nerve will die and a root canal will be needed. Root canals can be done through crowns as long as there is no decay under the crown. Keep the crown well flossed and brushed and you shouldn't need to have a new one placed.